Injection nozzle and a method for forming a fuel-air mixture

ABSTRACT

The present invention relates to a cylinder head for an internal combustion engine having a spark plug  3 , provided in combustion chamber  2 , and an injection nozzle  1  that has a housing end face  27  and a closure element  6  which is movable by an actuator and has a closure member  10 , the housing end face  17  of the injection nozzle  1  forming a common, planar surface with the closure member  10  in the closed state of the injection nozzle  1.

[0001] The present invention relates to a cylinder head for an internalcombustion engine, having a spark plug, provided in the combustionchamber, and an injection nozzle that has a housing end face and aclosure element that is movable by an actuator and has a closure member.The invention also relates to a method for forming an ignitable fuel-airmixture.

[0002] A method for forming an ignitable fuel-air mixture is alreadyknown from the German Patent 196 42 653 C1. In that case, an ignitablefuel-air mixture can be formed in the cylinders of direct-injectioninternal combustion engines, in that after a valve element has liftedoff from a valve seat surrounding a nozzle opening, thus releasing thenozzle opening, fuel is injected by an injector into each combustionchamber bounded by a piston. The opening stroke of the valve element andthe injection time are variably adjustable in order to permit aninternal mixture formation, optimized with respect to consumption andemissions, in each operating point of the entire characteristics mapunder all operating conditions of the internal combustion engine,particularly in stratified operation. In this case, a change in the jetgeometry due to combustion residues at the nozzle opening of theinjection nozzle, and thus an increased soot output as a result of poormixture formation in stratified lean operation, as well as the reductionin ignition reliability due to changing mixture quality at the sparkplug are possible. Moreover, increased components of unburned fuelresult due to thinning of mixture regions in stratified lean operation.Added to this are a wetting of the spark plug and consequently itsfailure due to carbon fouling, increased emissions because of incompletecombustion of the mixture state at the spark plug owing to statisticalscattering of the injection jet, and a collapse of the injection jetcaused by the combustion residues at the nozzle opening.

[0003] The object of the present invention is to ensure ignitionreliability in every operating point, and to avoid a change in thefuel-jet geometry due to combustion residues at the nozzle opening ofthe injection nozzle.

[0004] The objective is achieved according to the present invention inthat a housing end face of the injection nozzle forms a common, planarsurface with the closure member in the closed state of the injectionnozzle. Achieved by this is that the combustion residues, whichaccumulate in the region of the nozzle outlet, are broken up by theoutwardly opening valve member during the next injection process and aredetached by the emergent fuel jet. A growth in combustion residues inthe region of the outlet opening or nozzle opening is prevented in thismanner.

[0005] To this end, it is advantageous that the planar surface of theclosure member and the housing end face of the injection nozzle form acone-shaped lateral surface directed toward the combustion chamber, andthat the closure member has a conical sealing surface sealing the nozzleopening, and a cone-shaped lateral surface directed toward thecombustion chamber.

[0006] According to a further development, an additional possibility isfor the injection nozzle to have a housing wall whose inner side iscurve-shaped or conical and/or is constructed as a diffuser in theregion of the nozzle opening, and for the generatrix of the conicalsealing surface of the closure element to run tangentially or inparallel with respect to the curve-shaped or conical part of the housingwall, the generatrix of the fuel cone running in parallel with respectto the sealing surface or tangentially with respect to the curve-shapedpart of the housing wall and forming a right angle with the outerconical surfaces. Thus, the tangentially arranged sealing surfaces formno outward corners or edges on which combustion residues couldaccumulate. The fuel jet, continuously accelerated because of the nozzleshape, therefore emerges at right angles from the nozzle opening andcannot be influenced by existing combustion residues in the furtherregion of the outlet opening.

[0007] It is also advantageous that the fuel jet emerging from theinjection nozzle is more or less conical, and exhibits a constant jetangle α regardless of the position or setting of the closure element.Thus, the jet angle becomes independent of the fuel quantity introduced.The optimal mixture formation can therefore be ensured in everyoperating point.

[0008] Finally, according to a preferred specific embodiment of thedesign approach according to the present invention, a nozzle opening ofthe injection nozzle has a distance (A) of 1 mm to 8 mm to acombustion-chamber top, and a distance (B) of 10 mm to 15 mm to thespark plug, the injection pressure of the injection nozzle varyingbetween 100 bar and 300 bar or between 150 bar and 250 bar. The fuel-jetformation in the form of a toroidal swirl, necessary for an optimalmixture formation, is thereby achieved. In this context, the position ofthe spark plug and that of the fuel jet are decisive parameters.

[0009] Of particular importance for the present invention is that thecombustion-chamber top exhibits an angle β, the jet angle α being 10% to50% smaller than angle β of the combustion-chamber top. Wetting of thecombustion-chamber top, i.e. striking of the toroidal swirl on thecombustion-chamber top can thus be prevented.

[0010] In connection with the design and arrangement according to thepresent invention, it is advantageous that the fuel jet exhibits atleast one, or one inner and one outer toroidal swirl at the end of itscone envelope in the region of the piston. Optimal mixture formation isconsequently achieved in the entire combustion chamber.

[0011] It is also advantageous that the closure element is mounted in acoaxially rotational manner, and is movable at any time by the actuatorbetween 10 μm and 80 μm axially into the combustion chamber. Therefore,the rotatable closure member carries a speed component in thecircumferential direction into the fuel jet or fuel cone, thus improvingthe mixture formation and the fuel feed.

[0012] In addition, it is advantageous that the closure member has aconical sealing surface with an angle β between 70° and 90° or between70° and 85°, and a housing of the injection nozzle has a curve-shaped,parabolic or conical outlet cross-section, which together form thesealing seat or the sealing surface of the injection nozzle. Achieved bythis is that the nozzle opening continuously tapers toward the outlet,and the fuel jet is therefore continuously accelerated up to itsemergence. In this context, the fuel jet has a jet angle α regardless ofthe position of the closure element.

[0013] From the standpoint of process engineering, it is advantageousthat after the injection of each partial quantity, the closure member ofthe injection nozzle is able to be brought into its closed position. Thefuel feed, i.e. the two fuel pulses are thereby fed in a defined mannerat the respective instant, and therefore make a perceptible contributionto the optimal mixture formation. Closing of the nozzle opening withouta reduction in the fuel pressure at hand markedly improves therespective fuel pulse.

[0014] In this connection, it is also advantageous that 70% to 99% or80% to 99% of the entire fuel quantity is first introduced, and after0.05 ms to 0.4 ms or 1° to 5° arc of crankshaft rotation, the remainingpartial quantity is introduced, the injection cycle being completedbetween 50° and 5° arc of crankshaft rotation before top dead center.The main fuel quantity introduced first is optimally prepared by thesecond pulse, resulting in an unthinned, ignitable fuel-air mixture.

[0015] It is also advantageous that the fuel is introduced as a fuelcone, and at least one toroidal swirl is produced at the end of itscone-shaped lateral surface in the region of a piston. The toroidalswirl carries the introduced fuel inside and outside of the fuel coneinto the further regions of the combustion chamber, and above all intothe region of the spark plug.

[0016] Further advantages and particulars of the present invention areclarified in the patent claims and in the description, and are depictedin the Figures, in which:

[0017]FIG. 1: shows a sectional view of the injection nozzle of theinjector;

[0018]FIG. 2: shows a sectional view of one cylinder with piston,injection nozzle and spark plug;

[0019]FIG. 3: shows a sectional view of one cylinder with piston,injection nozzle spark plug and toroidal swirl.

[0020]FIG. 1 shows an injection nozzle 1 having a closure element 6 anda closure member 10. In addition, it has a cylindrical housing 17 formedabout a longitudinal axis, and a fuel chamber 18 situated betweenhousing wall 17 and closure element 6.

[0021] Closure element 6 is mechanically coupled at its upper end to anactuator (not shown) and to a return spring. The actuator is a piezoelement which expands under electrical voltage, and thereby ensures thelift of closure element 6. In addition to the spring energy, thepressure prevailing in fuel chamber 18 exerts a restoring force on anupper end face (not shown) of closure element 6. The imperviousness ofinjection nozzle 1 is therefore ensured at every instant.

[0022] Injection nozzle 1 has a nozzle opening 4, as well as closuremember 10. Nozzle opening 4 is first of all formed by a curve-shapedpart 25 at the lower end of housing wall 17. Curve-shaped part 25 ofhousing wall 17 is designed to be curve-shaped or parabolic incross-section on the inner side, i.e. at the end of fuel chamber 18.

[0023] Closure member 10 is formed as a double cone, that is to say, ithas a cone, i.e. a conical outer surface 26, both downward toward thecombustion-chamber side, as well as inward toward combustion chamber 2.This inner part represents a conical sealing surface 24 and, togetherwith inner, curve-shaped or parabolic part 25 of housing 17, forms asealing seat 14 and nozzle opening 4, respectively. In this context, thecone generatrix of cone 24 forms the tangent to inner, curve-shaped part25 of nozzle opening 4. Toward an outer side, i.e. toward housing endface 27 of injection nozzle 1, both sealing surfaces 24, 25 ultimatelyrun in parallel and form a right angle with outer generatrix 25 ofclosure member 10. End face 27 of housing wall 17 located in this regionis accordingly formed as a partial conical surface and has a planarjunction, that is to say, a common conical surface with a cone-shapedlateral surface, i.e. generatrix 26 in the closed state of injectionnozzle 1. Consequently, in the closed state, cone-shaped lateral surface26 is enlarged by the lower part of housing 17, i.e. end face 27. Thecross-section of fuel chamber 18 therefore tapers continuously towardsealing seat 14 and is equal to zero there in the closed state.

[0024] In response to an axial shift of closure element 6, closuremember 10 with its sealing surface 24 is lifted from curve-shaped part25 of housing 17 into combustion chamber 2, and therefore frees nozzleopening 4 for the fuel at hand. In this context, the opening stroke ofclosure element 6 and the duration of time that nozzle opening 4 isreleased determine the rate of fuel flow through nozzle opening 4, andconsequently the total amount or partial amount of fuel fed.

[0025]FIGS. 2 and 3 show one cylinder 12 of a direct-injection internalcombustion engine, in which a piston 9, with a cylinder head 13 closingcylinder 12, bounds combustion chamber 2. Injection nozzle 1 for fuel isarranged co-axially in cylinder head 13, with a clearance of 0 mm to 10mm to a cylinder axis 15. Cylinder head 13, i.e. a combustion-chambertop 8, is cone-shaped or roof-shaped in this region, injection nozzle 1being disposed in the highest point, i.e. in the region of the actualcone point or roof ridge.

[0026] A control unit (not shown) determines specifically for eachoperating point of the internal combustion engine, the instant, assignedto the position of a crankshaft, i.e. of a respective piston 9, for therelease of a nozzle opening 4 of injection nozzle 1. The fuel entersthrough it as fuel cone 7 in different partial sections of an injectioncycle, into combustion chamber 2.

[0027] An ignitable fuel-air mixture is formed in combustion chamber 2by the charge air, supplied to cylinder 12 through the intake port (notshown), and the injected fuel.

[0028] In stratified operation, the fuel is injected during thecompression stroke. With the injection process, a mixture cloud forms incombustion chamber 2 starting from injected fuel cone 7. Fuel cone 7forms an angle α between 70° and 90° which is always somewhat smallerthan angle β of combustion-chamber top 8. A spark plug 3 is positionedin combustion chamber 2 in such a way that its center axis is orientedmore or less normal to, i.e. with a deviation between 0° and 30°, tofuel cone envelope 7, which means fuel cone envelope 7 essentially doesnot moisten a ground electrode 3′ of spark plug 3. In response to aninjection pressure between 100 bar and 300 bar, so-called toroidalswirls 11, 11′ develop in the region of piston 9, starting from thefuel-jet generatrix (see FIG. 2). Toroidal swirl 11 develops due to arolling-up of fuel cone 7 starting from the generatrix of fuel cone 7,before fuel cone 7 strikes piston 9. A toroidal swirl 11 forms on theouter side of the cone over the cone periphery toward combustion-chambertop 8. With the developing toroidal swirl 11, that is to say, in theregion of toroidal swirl 11, the fuel is mixed with thecombustion-chamber air. Since outer toroidal swirl 11 develops abovefuel cone 7, an ignitable, unthinned fuel-air mixture is formed in theregion of spark plug 3, that is, at its electrode 3′. A second toroidalswirl 11′ develops within fuel cone 7. In this case, an ignitable,unthinned fuel-air mixture is produced in the region of injection nozzle1.

1. A cylinder head for an internal combustion engine comprising a sparkplug (3) provided in a combustion chamber (2), and comprising aninjection nozzle (1) having a housing end face (27) and a closureelement (6) that is movable by an actuator and has a closure member(10), wherein the housing end face (27) of the injection nozzle (1)forms a common, planar surface with the closure member (10) in theclosed state of the injection nozzle (1).
 2. An injection nozzle asrecited in claim 1, wherein the planar surface of the closure member(10) and the housing end face (27) of the injection nozzle (1) form acone-shaped lateral surface (26) directed toward the combustion chamber(2).
 3. The injection nozzle as recited in claim 1 or 2, wherein theclosure member (10) has a conical sealing surface (24) sealing a nozzleopening (4), and the cone-shaped lateral surface (26) directed towardthe combustion chamber (2).
 4. The injection nozzle as recited in one ofthe foregoing claims, wherein the injection nozzle (1) has a housingwall (17) whose inner side is curve-shaped or conical and/or is formedas a diffuser in the region of the nozzle opening (4).
 5. The injectionnozzle (1) as recited in one of the foregoing claims, wherein thegeneratrix of the conical sealing surface (24) of the closure element(6) runs tangentially with respect to a curve-shaped part (25) of thehousing wall (17).
 6. The injection nozzle (1) as recited in one of theforegoing claims, wherein the generatrix of a fuel cone (7) runs inparallel with respect to the sealing surface (24) or tangentially withrespect to the curve-shaped part (25) of the housing wall (17), andforms a right angle with the outer conical surfaces (26, 27).
 7. Theinjection nozzle (1) as recited in one of the foregoing claims, whereinthe fuel jet (7) emerging from the injection nozzle (1) is more or lessconical, and exhibits a constant jet angle α regardless of the positionor setting of the closure element (6).
 8. The injection nozzle (1) asrecited in one of the foregoing claims, wherein a nozzle opening (4) ofthe injection nozzle (1) has a distance (A) of 1 mm to 8 mm to acombustion-chamber top (8), and a distance (B) of 10 mm to 15 mm to thespark plug (3), the injection pressure of the injection nozzle (1)varying between 100 bar and 300 bar or between 150 bar and 250 bar. 9.The injection nozzle (1) as recited in one of the foregoing claims,wherein the combustion chamber top (8) exhibits an angle β, the jetangle α being 10% to 50% or 20% to 30% smaller than the angle β of thecombustion chamber top (8).
 10. The injection nozzle (1) as recited inone of the foregoing claims, wherein the fuel jet (7) has at least one,or one inner and one outer toroidal swirl (11, 11′) at the end of itscone envelope in the region of a piston (9).
 11. The injection nozzle(1) as recited in one of the foregoing claims, wherein the closureelement (6) is mounted in a coaxially rotational manner and is movableat any time via the actuator between 0 μm and 80 μm or between 10 μm and50 μm axially into the combustion chamber (2).
 12. The injection nozzle(1) as recited in one of the foregoing claims, wherein the closuremember (10) has the conical sealing surface (24) at an angle β between70° and 90° or between 70° and 85°, and the housing (17) of theinjection nozzle (1) has a curve-shaped or conical outlet cross-section(25), which together form a sealing seat (14) or the sealing surface(24) of the injection nozzle (1).
 13. A method for forming an ignitablefuel-air mixture in the combustion chamber (2) of a direct-injectioninternal combustion engine having the injection nozzle (1) which has theclosure member (10) and via which fuel is introduced in at least twopartial quantities into the combustion chamber (2), wherein the closuremember (10) of the injection nozzle (1) is able to be brought into itsclosed position after the injection of each partial quantity.
 14. Themethod as recited in claim 13, wherein 70% to 99% or 80% to 99% of theentire fuel quantity is first introduced, and after 0.05 ms to 0.4 ms or1° to 5° arc of crankshaft rotation the remaining partial quantity isintroduced, the injection cycle being completed between 50° and 5° arcof crankshaft rotation before top dead center.
 15. The method as recitedin claim 13 or 14, wherein the fuel is introduced as fuel cone (7), andat least one toroidal swirl (11) is produced at the end of itscone-shaped lateral surface (7) in the region of the piston (9).